Intra-cochlear electrode with a partially detachable hydrophilic segment for deferred self-positioning

ABSTRACT

A perimodiolar electrode for cochlear implantation includes an electrode carrier having a front end and a back end. The electrode carrier includes one or more contacts and a hydrophilic segment that swells after insertion in a cochlea and detaches at least in part from the carrier. In accordance with related embodiments, the hydrophilic segment may detach from the electrode carrier between the front end and the back end. The detached hydrophilic segment may surround the modiolus of a scala tympani of the cochlea or the inner wall of a scala tympani of the cochlea.

[0001] The present application claims priority from U.S. ProvisionalApplication No. 60/322,049 which is incorporated herein, in itsentirety, by reference.

TECHNICAL FIELD

[0002] The present invention relates to cochlear implants, and moreparticularly to a perimodiolar electrode designed for cochlearimplantation.

BACKGROUND

[0003] It is known to provide implants containing electrodes forstimulation of nerve tissue. Such implants include, for example,pacemakers, oral implants for stimulating muscle tissue in the mouth ofa subject or patient as well as nerve tissue associated with a subject'ssinus cavity and cochlear implants for stimulating the tissues of theinner ear. In the case of cochlear implants, the dynamic range ofstimulation is often limited and channel interaction often interfereswith the effectiveness of the implant. Channel interaction may be causedby the temporal integration of charges at the membrane level or by thefield overlap from individual electrodes.

[0004] Another problem associated with cochlear implants, is a tendencyfor the electrode to move after placement in the ear. Such movementdecreases the control of place stimulation, and consequently lowers thehearing performance of the subject. Movement of the electrode of acochlear implant may also contribute to unwanted and unnecessary nervestimulation such as facial nerve stimulation.

[0005] Recently, polydimethylsiloxane (PDMS)-based elastomers have beenused in a wide range of biomedical applications. Due to theirphysiological inertness, good blood compatibility, low toxicity, goodthermal and oxidative stability, low modulus and anti-adhesiveproperties. There has been an increasing interest in siliconerubber/hydrogels multi-component systems for various biomedicalapplications.

SUMMARY

[0006] In accordance with a first embodiment of the invention, aperimodiolar electrode for cochlear implantation includes an electrodecarrier having a front end and a back end. The carrier includes one ormore contacts and a hydrophilic segment that swells after insertion in acochlea and detaches at least in part from the carrier. In accordancewith related embodiments, the hydrophilic segment may detach from theelectrode carrier between the front end and the back end. The detachedhydrophilic segment may surround the modiolus of a scala tympani of thecochlea or the inner wall of a scala tympani of the cochlea. Inaccordance with further related embodiments, the electrode carrier mayinclude an elastomer. Similarly, the hydrophilic segment may include anelastomer and a metal-based catalyst. The elastomer may be siliconerubber or the elastomer may be polyurethane. The catalyst may beplatinum-based. In accordance with further related embodiments, thehydrophilic segment may include a hydrogel or the hydrophilic segmentmay include a hydrogel and an elastomer.

[0007] In accordance with another embodiment of the invention, a methodfor forming a cochlear implant electrode includes preparing ahydrophilic segment and placing the hydrophilic segment in a firstsection of an electrode mold. Electrical contacts are placed in a secondsection of the electrode mold and an elastomeric carrier is injectedinto the mold. In accordance with related embodiments, preparing ahydrophilic segment may include forming a hydrogel. Similarly, preparinga hydrophilic segment may include mixing a hydrogel and an elastomer. Inaddition, mixing a hydrogel and an elastomer may include mixing ahydrogel and liquid silicone rubber. In accordance with other relatedembodiments preparing a hydrophilic segment may include mixing anelastomer and a metal-based catalyst, and mixing an elastomer and ametal-based catalyst may include mixing liquid silicone rubber and aplatinum-based catalyst.

[0008] In accordance with a further embodiment of the invention, amethod for preparing a hydrophilic segment includes adding a metal-basedcatalyst to an elastomer and mechanically mixing the metal-basedcatalyst and the elastomer to form a cross-linked product. The mixtureis de-gassed and cured in a segment mold. The mixture is then immersedin a polymerization solution and suspended in a sealed glass reactor. Inaccordance with related embodiments, the method may also include raisingthe temperature to allow a monomer, initiator, and cross-linker to reactand removing monomers and unreacted hompolymers by soxlet extraction indistilled water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the invention will be more readily understood byreference to the following detailed description, taken with reference tothe accompanying drawings, in which:

[0010]FIG. 1 is a graphical illustration of an electrode with ahydrophylic segment prior to insertion into a cochlea in accordance withone embodiment of the invention;

[0011]FIG. 2 is a pictorial illustration of the electrode of FIG. 1;

[0012]FIG. 3 is a pictorial illustration of the electrode of FIG. 2showing initial swelling of the hydrophilic segment;

[0013]FIG. 4 is a pictorial illustration of an electrode in accordancewith an embodiment of the invention after insertion in a scala tympanimodel;

[0014]FIG. 5 is a pictorial illustration of the electrode of FIG. 4after the hydrophilic segment swells;

[0015]FIG. 6 is a flow chart illustrating a method for making aperimodiolar electrode in accordance with another embodiment of theinvention; and

[0016]FIG. 7 is a flow chart illustrating a method for making ahydrophilic segment in accordance with a further embodiment of theinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0017] The present application pertains to the formation of implantableapparatuses such as pacemakers, cochlear implants, and other nervestimulating devices. In accordance with the invention,polydimethylsiloxane (PDMS)-based elastomers are used to aid in thepositioning of the implantable device subsequent to insertion into thebody of a subject or patient.

[0018] Modeling of intra-cochlear stimulation and animal EABR dataindicates that an electrode (or electrode array) positioned close to theinner wall of the scala tympani would be beneficial to theneuro-stimulation of cochlea implants (hence the name perimodiolarelectrode). There is a consensus that such a perimodiolar electrodewould lower psyco-accoustic threshold, increase the dynamic range ofstimulation, and reduce channel interaction. Other potential benefitsexpected from a perimodiolar electrode array include reduced powerconsumption to drive the implant, reduced side effects for the subjector patient, implementation of innovative stimulation schema, and betterplace coding of frequency. Further, a perimodiolar electrode would allowa larger number of electrodes to be used effectively. It is hoped thatan increase in the control of place stimulation would contribute towardraising the level of subjects or patients with poor hearing performance.An additional, potential benefit expected from a perimodiolar electrodeis the side effect of unwanted and unnecessary stimulation would bereduced (especially reduced facial nerve stimulation).

[0019]FIGS. 1 and 2 illustrate a perimodiolar electrode with ahydrophylic segment prior to insertion into a cochlea in accordance withone embodiment of the invention. In accordance with this embodiment, theperimodiolar electrode 101 is designed for implantation into the cochleaof a subject and includes an electrode which can surround the modiolusor the inner wall (also called the medial wall) of the scala tympani.The electrode 101 includes a front end 104 and a back end 105. Theelectrode 101 also includes a hydrophilic segment 102 that is initiallysubstantially fully connected to an electrode carrier 103. The crosssectional shape of the electrode 101 may be ellipsoid, round, somewhatrectangular, or any combination of the above. Similarly, the electrode101 may be tapered or un-tapered along its length. When the hydrophilicsegment 102 is substantially fully connected to the electrode carrier103, the overall electrode 101 appears as a single unit, as shown incross section A-A′ of FIG. 1. When the electrode 101 is fully orpartially introduced in the scala tympani spiral, it lays against theouter wall of the lumen.

[0020]FIGS. 3 and 5 illustrate that at some time after insertion intothe scala tympani, the hydrophilic segment 102 of the electrode 101begins swelling. The swelling of the hydrophilic polymer causes anincrease in diameter as well as an elongation of the hydrophilic segment102. Eventually, the swelling hydrophilic segment 102 detaches itselffrom the electrode carrier 103, except at the front end 104 and back end105, as shown in FIGS. 3 and 5. The swelling segment of the electrodestays in close contact with the outer wall of the scala tympani.Elongation of the hydrophilic segment 102 causes the electrode 101 toposition itself against the inner wall of the scala tympani as shown inFIG. 5.

[0021] The shape of the swelling hydrophilic segment 102 is determinedby the mold that receives the injection of the polymer or othercomposition from which the segment it is formed. The shape may be thatof a half circle, an ellipsoid, a rectangle, or any other shape whichmay promote or restrict the swelling properties of the segment inrelation to the electrode carrier. The increase in volume of theswelling polymer is a control parameter and may vary between 10% and 60%depending on the hydrophilic mixture. The elongation of the swellingpolymer may be anywhere between 10% and 50%. The relative size of theswelling polymer compared to the electrode carrier may be arbitrary.

[0022] In its final state, the electrode 101 consists of two connectedbranches and as shown in FIG. 3. The electrode carrier 103 and thehydrophilic segment 102 both have a front-end connection 301 and aback-end connection 302. The front-end connection 301 and back-endconnection 302 consist of any means which keeps the electrode carrier103 and the hydrophilic segment 102 connected before, during, and aftercompletion of swelling while permitting detachment of the hydrophilicsegment 102 over at least part of the distance between the front-endconnection 301 and the back-end connection 302. Such a connectionincludes but is not limited to polymer bonding, clip, pin-notch system,or any means as deemed profitable.

[0023] In the embodiments described herein, the front-end connection 301is dis-connectable for the purpose of ex-plantation of the electrode 101when necessary. Thus, when the implant needs replacement, thehydrophilic segment 102 is easily dis-connectable. In order to achievedis-connectibility, the hydrophilic segment 102 and the electrodecarrier 103 may be joined by a bare PtIr ribbon section, which comes outof the hydrophilic segment 102 and is lodged snuggly or loosely in anoriented silicone cavity molded on the electrode carrier 103. In case ofrevision surgery, the hydrophilic segment 102 can be dislocated at thefront-end connection 301 by simply pulling back on the hydrophilicsegment 102 with sufficient force. The front-end connection 301 may beany other system known in the art and deemed advantageous. The back-endconnection 302 may be accomplished through polymer bonding. Similarly,the back-end connection 302 may be accomplished through a medical gradetitanium clip such as those produced by Heinz Kurz GmbH in Dusslingen,Germany. The branches may also be attached with a PtIr wire, a siliconering, or surgical sutures.

[0024] As can be seen in FIGS. 1, 2 and 3, the front end 104 generallyprojects beyond the hydrophilic segment 102 by some distance. However,the length ratio between the front end 104 and hydrophilic segment 102may be anywhere from 0.3 to 3. The electrode carrier 103 usuallyincludes a single row of contacts 106 facing the modiolus and the numberof contacts 106 may be arbitrarily fixed. Further, the electrode 101 mayhave double or more contacts to increase the surface area of theelectrode and reduce the impedance. The contact distribution between thefront end 104 and the rest of the electrode 101 can be arbitrary. For ann contacts electrode, the front end 104 may receive anywhere from 0.1 nto 0.8 n of the contacts, as deemed advantageous for stimulation. It mayalso be that the electrode 101 is built with no front end 104 and thatthe hydrophilic segment 102 converges at the tip of the electrode 101.In addition, the contact spacing on the front end 104 may be equal,logarithmic, or equal and logarithmic. Dummy contacts or markers can beplaced between the last contact on the electrode (most basal) and for adistance of up to 15 mm. Dummy contact or marker separation isarbitrary. The role of the dummy contact or marker is to give anindication of the insertion depth of the electrode to the surgeon. Thedummy contact or marker may be shape coded to indicate distance alongthe array without having to count the number of interval between thecontacts.

[0025]FIG. 6 is a flow chart illustrating a method for making aperimodiolar electrode in accordance with another embodiment of theinvention. In process 601 a hydrophilic segment is prepared and thenplaced 602 in a first section of an electrode mold. Preparing ahydrophilic segment may include forming a hydrogel. (For purposes of thepresent application, the term “hydrogel” refers to a coherentthree-dimensional polymeric network that can imbibe large quantities ofwater without the dissolution of the polymer network.) Preparing ahydrophilic segment may further include a mixing a hydrogel and anelastomer. In addition, mixing a hydrogel and an elastomer may includemixing a hydrogel and liquid silicone rubber. Similarly, preparing ahydrophilic segment may include mixing an elastomer and a metal-basedcatalyst, and mixing an elastomer and a metal-based catalyst may includemixing liquid silicone rubber and a platinum-based catalyst. Electricalcontacts are placed 603 in a second section of the electrode mold and anelastomeric carrier is injected 604 into the mold.

[0026] As discussed above, the hydrophilic segment can be prepared froma hydrogel or a multi-component system of hydrogel and elastomer(silicone rubber or polyurethane). The multi-component system may befabricated by co-polymerization, grafting, blending, simultaneousinterpenetrating polymer network, and sequential interpenetratingpolymer network. An interpenetrating polymer network (“IPN”) is definedas an intimate combination of two or more polymers, at least one ofwhich is synthesized or cross-linked in the immediate presence of theother. The cross linking of at least one of the polymer systemsdistinguishes an IPN from an ordinary blend or a co-polymer.

[0027]FIG. 7 is a flow chart illustrating a method for making ahydrophilic segment in accordance with a further embodiment of theinvention. In accordance with this embodiment, the hydrophilic segmentis prepared by adding, in process 701, a metal-based catalyst to anelastomer. For example, liquid silicone rubber (“LSR”) may be mixed witha platinum-based catalyst. The metal-based catalyst and the elastomerare mechanically mixed 702 to form a cross-linked product. The mixtureis de-gassed in process 703 and injected into a mold with a pre-designedcavity shaped for the hydrophilic segment. After a curing (andoptionally, post-curing) the mixture in the segment mold in process 704,the product is immersed 705 for approximately twenty-four hours at roomtemperature in a polymerization solution that may include acrylic acidor acrylamide monomer. The swollen hydrophilic segment samples aresuspended 706 in a sealed glass reactor. The temperature is raised 707and kept at a definite temperature to allow the monomer, initiator, andcross-linker to react. The monomers and unreacted hompolymers areremoved 708 by soxlet extraction in distilled water. As described abovewith respect to the embodiment of FIG. 6, the hydrophilic segment isplaced in a first part of a mold, and, after fixation of wires inside asecond part of the mold, LSR is injected in to the mold to produce thefinal electrode.

[0028] There are several advantages of the design disclosed in thepresent application over prior art: a) the electrode carrier andhydrophilic polymer are and remain attached during the insertionprocess; b) a surgeon does not have to perform any additionalpositioning since the electrode is self positioning post operatively; c)the connection to the electrode modiolus is independent of morphology;d) the front end of the electrode has less of a tendency to perforatethe basilar membrane during the positioning process; e) no special toolsare needed for insertion or positioning; f) the electrode and theinsertion aperture on the bony promontory may remain small in diameter;and g) a section of the electrode (e.g., the front end) may be deeplyinserted in the cochlear.

[0029] While the invention has been described in connection withspecific embodiments thereof, it will be understood that it is capableof further modification. This application is intended to cover anyvariation, uses, or adaptations of the invention and including suchdepartures from the present disclosure as come within known or customarypractice in the art to which invention pertains.

What is claimed is:
 1. A perimodiolar electrode for cochlearimplantation comprising: an electrode carrier having a front end and aback end, the carrier including one or more contacts and a hydrophilicsegment that swells after insertion in a cochlea and detaches at leastin part from the carrier.
 2. A perimodiolar electrode according to claim1, wherein the hydrophilic segment detaches from the electrode carrierbetween the front end and the back end.
 3. A perimodiolar electrodeaccording to claim 1, wherein the detached hydrophilic segment surroundsthe modiolus of a scala tympani of the cochlea.
 4. A perimodiolarelectrode according to claim 1, wherein the detached hydrophilic segmentsurrounds the inner wall of a scala tympani of the cochlea.
 5. Aperimodiolar electrode according to claim 1, wherein the electrodecarrier further comprises an elastomer.
 6. A perimodiolar electrodeaccording to claim 1, wherein the hydrophilic segment comprises anelastomer and a metal-based catalyst.
 7. A perimodiolar electrodeaccording to claim 6, wherein the elastomer is silicone rubber.
 8. Aperimodiolar electrode according to claim 6, wherein the elastomer ispolyurethane.
 9. A perimodiolar electrode according to claim 6, whereinthe catalyst is platinum-based.
 10. A perimodiolar electrode accordingto claim 1, wherein the hydrophilic segment includes a hydrogel.
 11. Aperimodiolar electrode according to claim 1, wherein the hydrophilicsegment includes a hydrogel and an elastomer.
 12. A perimodiolarelectrode according to claim 11, wherein the elastomer is siliconerubber.
 13. A method for forming a cochlear implant electrode, themethod comprising: preparing a hydrophilic segment; placing thehydrophilic segment in a first section of an electrode mold; placingelectrical contacts in a second section of the electrode mold; andinjecting an elastomeric carrier into the mold.
 14. A method accordingto claim 13, wherein preparing a hydrophilic segment includes forming ahydrogel.
 15. A method according to claim 13, wherein preparing ahydrophilic segment includes a mixing a hydrogel and an elastomer.
 16. Amethod according to claim 15, wherein mixing a hydrogel and an elastomerincludes mixing a hydrogel and liquid silicone rubber.
 17. A methodaccording to claim 13, wherein preparing a hydrophilic segment includesmixing an elastomer and a metal-based catalyst.
 18. A method accordingto claim 17, wherein the mixing an elastomer and a metal-based catalystincludes mixing liquid silicone rubber and a platinum-based catalyst.19. A method for preparing a hydrophilic segment, the method comprising:adding a metal-based catalyst to an elastomer; mechanically mixing themetal-based catalyst and the elastomer to form a crossed linked product;de-gasing the mixture; curing the mixture in a segment mold; immersingthe mixture in a polymerization solution; and suspending the mixture ina sealed glass reactor.
 20. A method according claim 19, furthercomprising: raising the temperature to allow monomer, initiator, andcross-linker to react; and removing the monomers and unreactedhompolymers by soxlet extraction in distilled water.